This invention relates to a tangentially fired furnace, more specifically to a modification of a tangentially fired furnace to reduce pollutant generation.
The Clean Air Act and the Amendments of 1990 have imposed increasingly stringent controls on the industrial generation of pollutants such as NO and NO.sub.2 (NOX) and SO.sub.2 and SO.sub.3 (SOX). These pollutants are emitted in large quantities from combustion operations carried out in electric utility and other industrial furnaces. To reduce the formation of these pollutants, methods and apparatus have been developed.
In the oxidant predilution method, oxygen concentration in the combustion air supply is reduced by mixing in a quantity of inert gas. Commonly used diluents are nitrogen from an external source or furnace flue gas in which oxygen has been depleted. From 5% to 20% flue gas recirculation or nitrogen is commonly introduced into the air supplied to the furnace windbox for combustion of fuel. The diluent lowers the peak flame temperature in the primary fuel burning zone, which reduces the generation of pollutants.
In the "overfire air" method, the quantity of combustion air supplied in close proximity to the fuel introduction location in the furnace firing chamber is reduced relative to prior practice. This causes a reduction in the concentration of oxygen at the primary burning location and lowered flame temperature, resulting in reduced pollutant generation. Special air supply ports are installed above the fuel introduction locations to make up the deficit in air required for complete combustion of the fuel introduced. This air is called overfire air.
These known methods and the apparatus required to practice them are sophisticated, mechanically complex, and costly. What is needed is a method and apparatus for inexpensively modifying a tangentially fired furnace to accomplish pollutant reduction.